This invention relates to fixtures for supporting and aligning components of cathode ray tube envelopes during fabrication and more particularly to such fixtures for supporting the envelopes in a face down position.
Conventional cathode ray envelopes are fabricated from a faceplate, having the screen of the tube, and a funnel. After the internal screen components are fabricated on the faceplate, the funnel is sealed to the faceplate usually by frit sealing. The frit material, which is typically high lead glass, is applied to an edge of either the funnel or the faceplate. This edge then is placed in contact with the other component in an aligned relationship. The abutting faceplate and funnel are then heated and cooled which causes the frit material to bond the two components.
Various structures have been devised for maintaining the faceplate and funnel in an aligned abutting relationship during the application of the heat which seals them together. For example U.S. Pat. No. 3,118,662 issued on Jan. 21, 1964 to Gardner Fassett et al. discloses fixtures for fabricating round face cathode ray tubes both the face up and the face down positions. Certain problems develop with respect to the face down method of frit sealing. In particular, the fixture studs which are to be used to support the tube often cause the deformation of the face under the high sealing temperatures. During the high temperature sealing, the weight of the tube on the studs would leave marks or dents on the face of the tube. When rectangular face tubes came into use, such a fixture which utilizes only two orienting structures for aligning the faceplate with respect to the funnel became impractical.
Because of these problems, conventional frit sealing fixtures for rectangular cathode ray tubes are similar to that shown in U.S. Pat. No. 3,787,937 issued on Jan. 29, 1974 to Kazimir Palac. This structure maintains the faceplate and funnel in a face up position during assembly and utilizes three alignment structures to orient and maintain both of the components in an aligned relationship. However, problems also developed with the face up frit sealing method. Moisture within the tube often condenses on the inside of the faceplate contaminating the phosphorescent coatings. Such fixtures have a design limitation on the neck support force subject to the neck glass strength. The funnel neck would often distort under the weight of the tube during the heating steps. Furthermore, several different size cathode ray tubes may be fabricated using the same faceplate dimensions but various funnel dimensions. In this case, a separate face-up fixture has to be fabricated to accomodate the different funnel sizes of each tube style.